1. Field of the Invention
The present invention relates generally to analog to digital converters (ADC) communications receiver, more specifically to extending a dynamic input range of an ADC.
2. Related Art
An analog to digital converter (ADC) is an electronic circuit that converts an analog input to a digital output signal. The ADC includes one or more quantization levels to produce the digital output signal. Each quantization level may be assigned to a combination of bits, referred to as a codeword. The ADC selects a corresponding one of the quantization levels as a representation of the analog input. The ADC assigns the codeword corresponding to a selected quantization level to the digital output signal to convert the analog input to a digital representation.
A ratio between a most miniscule nonzero quantization level and a maximum quantization level may be referred to as a dynamic input range of the ADC, r, such that the dynamic range r is greater than or equal to one. Generally, the dynamic input range of the ADC is determined such that a maximum value of the analog input is less than or equal to the maximum quantization level, and/or a minimum value of the analog input is greater than or equal to the minimum quantization level. However, the minimum value of the analog input and/or the maximum value of the analog input may fall below the minimum quantization level and/or rise above the maximum quantization level, respectively, causing the ADC to saturate or clip. When clipping occurs, the digital output signal no longer accurately represents the analog input.
A conventional ADC may attenuate the analog input before conversion to the digital representation. Attenuation of the analog input in this manner ensures the maximum value level of the analog input does not exceed the maximum quantization level too often or by too much. As a result of this attenuation, each quantization level of the conventional ADC is required to convert a greater range of the analog input as observed prior to the attenuation, thereby reducing a resolution of the conventional ADC. This reduction in resolution of the conventional ADC corresponds to an increase in quantization noise of the conventional ADC relative to the analog input prior to its attenuation. To avoid this increased quantization noise in the presence of the attenuation, a number of the quantization levels of the conventional ADC may be increased in proportion to the attenuation. Increasing the number of quantization levels in this manner increases the dynamic input range of the conventional ADC. However, increasing the number of the quantization levels increases an area and a power consumption of the conventional ADC. Further, increasing the number of the quantization levels may cause an increase in a number of bits to be processed by signal processors that rely on the conventional ADC to provide an input.
Therefore, what is needed is an ADC with an extended dynamic input range but achieved without proportionately increasing the number of the quantization levels and/or reducing the effective resolution of the ADC.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.